After logged into your NetworkSolutions account, click on View Domain Name List link on left.

Click on the domain name you want to change.

The Domain Details section displays different options. Select the radio button next to Custom DNS Setting and click on the Apply Change button. (Note: If radio button DNS Settings was already selected, then click on Edit DNS.)

Next you will see Edit DNS page. On this page click on the Continue button (under the section Move DNS to a New Name Server). In the next page, after reading the confirmation warning, click on the Continue button.